This application is based on and claims priority of Swedish Patent Application No. 0001434-0, filed Apr. 14, 2000, the disclosure of which is incorporated by reference herein.
The present invention relates to a rock-crushing rotary drill bit and a check valve therefor.
The placement of one or more nozzle-carrying passageways in a rotary drilling bit to conduct air or other drilling fluids from the central bore of the bit to the rotating cutters is well known. The drilling fluid thus directed serves to cool the cutters and to carry cuttings away from the cutters. However, the presence of these passageways makes it possible for cuttings and other foreign materials to enter the interior of the bit through the nozzle(s) when the circulation of the drilling fluid ceases and thus to impair the further operation of the bit, e.g., foul the bearings of the bit. This problem has been dealt with by placing check valves or filters in the interior bore and passageways of rotary drill bits. A drawback of such prior rotary drill bits is that fluid may still rise upwardly into the drill bit through the nozzle if the surrounding pressure during drilling is greater than the pressure in the drill bit, for example when the flow of flushing medium is terminated during the addition of additional sections of the drilling string.
In U.S. Pat. No. 3,685,601 that problem has been dealt with by means of a check valve positioned in the nozzle itself. The check valve comprises a spring-loaded closure plate hingedly mounted in a hollow body that forms part of the nozzle. The hinged closure plate opens and closes in an oscillating manner in the channel of the nozzle dependent on the direction of the flushing medium. Use of this type of hinged check valve has been insufficient due to premature breakages, e.g., due to metallic fatigue of the hinge.
Other prior art rotary drill bits shown in U.S. Pat. Nos. 4,457,384 and 3,089,551 are exemplary of check valves positioned in the central bore of the bit at the level of the external conical thread of the bit, thus allowing dirt to enter the bit.
One object of the present invention is to provide a rotary drill bit, which enjoys the advantages associated with prior techniques.
Another object of the present invention is to provide a rotary drill bit, which has an extended life.
Still another object of the present invention is to provide a rotary drill bit, which has a check valve with an inertia such that the bearing of the drill bit is flushed substantially clean before drilling is resumed.
Still another object of the present invention is to provide a rotary drill bit, which has a robust check valve that does not break due to metallic fatigue.
Still another object of the present invention is to provide a rotary drill bit, which minimizes the formation of cavitation in the flow of flushing fluid and thus reduces blasting damage.
A rock-crushing rotary drill bit comprises a body forming at least one leg, and a rotatable roller rotatably mounted on the at least one leg by bearings. The roller includes rock-crushing elements. The body further includes an external thread adapted for connecting the roller to a drill tube. A main channel in the body conducts flushing medium. A first flushing channel passes through the leg and communicates with the main channel for conducting part of the flushing medium to flush the bearings. A second flushing channel communicates with the main channel and includes a discharge recess for discharging another part of the flushing medium. The flushing recess defines a linear center axis. A nozzle is disposed at a downstream end of the discharge recess for directing flushing medium in a direction to flush away cuttings. A valve element is disposed at an upstream end of the discharge recess and includes a guide structure for guiding the valve element for linear movement along the center axis. The valve element is spring-biased to a closed state for closing the discharge passage, and is yieldable in response to fluid medium pressure acting thereagainst, for opening the discharge recess.
The invention is also directed to a check valve per se, wherein the valve element, and biasing spring, are mounted within a house that carries the nozzle at one end thereof.